Method and device for assessing the risk of fluid leakage in a heat exchanger with sensor

ABSTRACT

A method and device, for a heat exchanger which is provided with gaskets, for assessing and detecting the risk of fluid leakage in the heat exchanger due to worn-out gaskets. In the heat exchanger, a heat transfer plate ( 5 ) with gasket ( 6 ) is provided with a pressure sensor ( 15 ) which monitors the pressure between the plate ( 5 ) and the gasket ( 6 ). A further sensor is adapted to the heat exchanger for monitoring the pressure of the fluid entering the heat exchanger.

This application is a divisional (and claims the benefit of priorityunder 35 USC 120-121) of U.S. application Ser. No. 11/597,945, filedNov. 28, 2006 now U.S. Pat. No. 7,568,516, which claims the benefitunder 35 USC 371 of PCT International Application No. PCT/SE2005/000702,filed on May 17, 2005, and also claims the benefit of foreign prioritySwedish Application No. 0401434-6, filed Jun. 4, 2004. The disclosuresof the prior applications are considered part of (and are herebyincorporated by reference in) the disclosure of this application.

FIELD OF THE INVENTION

The present invention relates to an apparatus and method, for assessingthe risk of fluid leakage in a plate heat exchanger provided withgaskets.

Heat exchangers provided with gaskets traditionally comprise a number ofheat transfer plates which together with intermediate gaskets constitutea plate package. The gaskets are normally held in position by, forexample, adhesive bonding or by the plate package being clamped betweentwo end-plates or pressure plates pressed together so that the gasketsare fixed and held in position. To render a plate heat exchanger easy todismantle and service, e.g. with a view to remedying leakage due todefective or worn-out gaskets, the end-plates or pressure plates areusually connected mechanically to the plate package and supported by aframe. Worn-out and defective gaskets are a common cause of fluidleakage in a heat exchanger and it is therefore usual that the gasketsneed replacing at regular intervals of time.

BACKGROUND TO THE INVENTION

Heat exchangers comprising various types of sensors for measuringvarious operating parameters such as the temperature and pressure of thefluid passing through a heat exchanger are known. Sensors for detectingfluid leakage in a heat exchanger are also known.

British patent specification GB 2062833-A describes a heat exchangerfor, inter alia, a health-damaging fluid. The heat exchanger is made upof heat exchanger plates which have portholes, are welded together inpairs and are installed with gaskets between each pair of welded plates.The region round the ports comprises a first gasket which is situatedclose to the port orifice and thereby has fluid contact round it, and asecond gasket which is situated outside the first gasket so that a spaceis formed between the gaskets. In the event of leakage through the firstgasket, fluid enters the space between the gaskets and is therebyprevented from mixing with other fluid in the heat exchanger. A sensoris installed in such a way that it extends through the second gasket andinto the space between the gaskets. The purpose of the sensor is tomonitor and indicate fluid entering the space between the gaskets, whichwill mean that the first gasket nearest to the port has failed and needschanging. The disadvantage of the invention according to GB 2062833-A isthat only when the gasket has failed and leakage in the heat exchangerhas already occurred does the sensor provides an indication.

European patent specification EP 0520380-A1 describes a gasket for avehicle engine, which gasket comprises sensors for pressure monitoring.The sensor is situated between two gasket halves together with sealmeans for preventing direct contact with fluid. The disadvantage of theinvention according to EP 0520380-A1 is the complicated gasket structurewhich means that the gasket is expensive to manufacture and involves anumber of manufacturing steps to finished product. A furtherdisadvantage of gaskets made up of a number of parts is that the partsmay delaminate from one another, which may result in the gasket startingto leak. A further disadvantage is that the sensors are only intended tomeasure pressure in the gasket, and the arrangement is not equipped forassessing the risk of leakage due to the gasket having failed. A furtherdisadvantage of the gasket is that its configuration is such that it isimpossible to apply it to heat exchanger plates, since it is designed toseal between two relatively large flat surfaces and not for fitting intoa gasket recess in a heat exchanger plate.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a method whereby it ispossible, in a heat exchanger provided with gaskets, to determine whengasket replacement is required in order to prevent leakage through agasket taking place because of failure or wear, and whereby theaforesaid problems are eliminated.

A further object of the present invention is to provide a method formonitoring gasket material functionality in a heat exchanger providedwith gaskets.

The aforesaid and other objects are achieved according to the inventionby the method described in the introduction being provided with thecharacteristics indicated by claim 1.

An advantage afforded by a method according to the characterising partof claim 1 is the possibility of assessing on the basis of thecompression pressure monitored the risk of fluid leakage in a plate heatexchanger provided with gaskets. It thus becomes possible to predictwhen gaskets in heat exchangers need replacing in order to preventgaskets failing during operation.

A further object of the present invention is to provide, for a heatexchanger provided with gaskets, a method for indicating the risk offluid leakage, which method is economically advantageous relative to thecost of replacing gaskets in a heat exchanger when leakage through thelatter's gaskets has occurred. Another object is that the method shouldbe easy to apply and result in savings of time relative to comparabletechniques.

Preferred embodiments of the method according to the invention have beenfurther provided with the characteristics indicated by subclaims 2-6.

According to another embodiment of the method according to theinvention, the compression pressure of the gasket material is registeredby means of a first sensor. Pressure changes in the heat exchanger canthus be detected at an early stage in the operation of the heatexchanger. Pressure changes may for example be due to gasket wear or toplates not being firmly clamped between the end-plates or pressureplates. Monitoring pressure changes at an early stage minimises the riskof leakage occurring through or past the gaskets.

According to a further embodiment of the method according to theinvention, the pressure of the fluid in the heat exchanger is measuredby means of a second sensor which also gives the pressure of the fluidrelative to the gasket material. Pressure changes in the aforesaid fluidare thus detected. Using such a second sensor also makes it possible tocheck that the heat exchanger is not overpressured, i.e. not pressurisedbeyond a predetermined upper limit value. Supervising the pressure ofthe fluid in the heat exchanger, inter alia so that overpressure can beavoided, makes it possible to lengthen the life of the heat exchangerand its components by avoiding wear due to high pressure. To ensurecorrect monitoring of the fluid pressure, the second sensor is installedin such a way that it has fluid contact with the fluid in the heatexchanger. The highest pressure in the fluid of a heat exchanger isnormally at the inlet to the heat exchanger, after which the pressuredeclines through the heat exchanger pro rata to the distance from saidinlet This means that the location of the second sensor need not beconfined to the heat exchanger itself. Instead, the sensor may besituated at any desired point along the flow path of the fluid to theheat exchanger from the last component of the heat exchanger system. Thelast component of the heat exchanger system is defined as the lastcomponent which has the possibility of influencing the characteristic ofthe fluid entering the heat exchanger, i.e. the pressure. This lastcomponent may for example be a pump which supplies the heat exchangerwith fluid.

In a further embodiment of the method according to the invention, thevalues registered by the various sensors are processed in a processor.The values registered are used to calculate a reference value, aso-called differential pressure value, which is compared with apredetermined set-value. This comparison makes it possible to detectquickly any deviations which might be due to a gasket being worn out orabout to fail. Such deviation will activate an indicator to attractattention, e.g. a lamp or some other signal. Gasket replacement in theheat exchanger can thus be effected before leakage occurs.

A further object of the present invention is to provide a device for aheat exchanger provided with gaskets which enables simultaneousmonitoring of the fluid pressure of the heat exchanger and thecompression pressure of the gaskets.

The aforesaid and other objects are achieved according to the inventionby the heat exchanger described in the introduction being provided withthe characteristics Indicated by claim 1.

An Advantage afforded by a device according to the characterising partof claim 1 is the possibility of measuring in the heat exchanger boththe fluid pressure of the fluids and the compression pressure of thegaskets. It thus becomes possible to measure the difference between theaforesaid [measurements] and predetermined set-values so that deviationsof the pressure values measured can be detected. Such deviations may forexample indicate that a gasket is worn out and needs replacing iffailure or leakage through it is not to occur.

A further object of the present invention is to provide in a heatexchanger provided with gaskets a device for indicating the risk offluid leakage, which device is economically advantageous relative to thecost of replacing gaskets in a heat exchanger when leakage has occurredthrough the latter's gaskets. Another object is that the device shouldbe easy to construct and also result in savings of time relative tocomparable techniques.

Preferred embodiments of the device according to the invention have beenfurther provided with the characteristics indicated by subclaims 2-6.

In a further embodiment of the device according to the invention, thefirst sensor is situated in a recess arranged for a gasket in the plateand is adapted to monitoring the pressure between the gasket and theplate. The compression pressure of the gasket can thus be monitored. Anadvantage of situating the sensor in the gasket recess is that thesensor is protected from extraneous influences. A further advantage ofsensors being situated in gasket recesses is that when the plates arepressed together the sensors are clamped and positioned between gasketand plate, thereby holding the sensors in position.

In a further embodiment of the device according to the invention, thefirst sensor for monitoring the compression pressure of the gasket issituated between the heat transfer plates which together form a flowchannel. This channel may be the channel which is the first recipient ofthe hot fluid entering the heat exchanger. This means that it is in thischannel that the incoming fluid is at its highest temperature in theheat exchanger and hence also has the greatest effect on the gaskets.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the device and the method according to theinvention are described below with reference to the attached schematicdrawings, which depict only the components which are necessary forunderstanding the invention.

FIG. 1 depicts schematically a heat exchanger system comprising a heatexchanger with various pipe connections and a component which by itsfunction is the last component which can influence the characteristic ofthe incoming fluid, i.e. the pressure of the fluid.

FIG. 2 depicts part of a heat exchanger according to the invention, witha frame plate and a pressure plate and, between these, a number of heattransfer plates and gaskets. To facilitate comprehension, the heattransfer surfaces of the first three plates are turned towards thereader.

FIG. 3 depicts a transverse cutaway view of a plate and a gasket with asensor situated between the plate and the gasket.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

FIG. 1 depicts a heat exchanger system (1) with inter alia a heatexchanger (2). The heat exchanger (2) comprises a frame plate (3)comprising inlet and outlet ports, see FIG. 2, and a pressure plate (4).A number of heat transfer plates (5 a, 5 b, 5 c and so on) with gaskets(6) are situated between said frame plate (3) and pressure plate (4). Inthe ensuing text, the heat transfer plates (5 a, 5 b, 5 c and so on)will only be referred to as plates (5 a, 5 b, 5 c and so on). FIG. 2makes it clear how the gaskets (6) of the heat exchanger (2) arearranged by showing three of the plates (5 a-5 c) turned 90 degreesabout a vertical centreline (14) so that the heat transfer surfaces (10)of the plates (5) are turned towards the observer. In addition, thefluid flow is indicated schematically in the diagram by arrows (7).

In the preferred embodiment of the invention, each plate (5) has fourports (11 a, 11 b, 11 c and 11 d) located in such a way that each cornerportion of a plate (5) comprises a port. Each plate (5) furthercomprises a heat transfer surface (10) and two longitudinal edges, viz.a left edge (8) and a right edge (9), a top edge (12) and a bottom edge(13). The centreline (14) extends from the top edge (12) to the bottomedge (13) (between the two upper ports (11 a and 11 b) and between thetwo lower ports (11 c and 11 d)) and divides the plate (5 c) into twohalves.

The gasket (6) is situated in a gasket recess (not depicted in thedrawing) in the plate (5) and extends round the heat transfer surface(10) of the plate (5) and round the latter's ports (11 a, 11 b, 11 c and11 d).

The plates in FIG. 2 are shown numbered from the left, the first plate(5 a) being situated nearest to the frame plate (3). A sensor (15 a) issituated on the third plate (5 c). The sensor (15 a), see FIG. 3, issituated between the gasket (6) and the plate (5 c) in such a way thatit abuts against both the gasket (6) and the plate (5 c). The sensor (15a) is positioned at the upper left region of the plate (5 c), along thelongitudinal left edge (8) and lower than the upper left port (11 a). Inthis region the gasket (6) is subject to the largest of the variousfatigue factors which are all contributory causes to the possibility ofa gasket failing. Examples of the fatigue factors are temperaturefluctuations, friction, fluid contact and oxygen contact from theoutside of the heat exchanger. Oxygen contact will dry the gasket (6),thereby contributing to the gasket (6) initially beginning to crackbefore subsequently failing completely.

In an alternative embodiment of the invention, a sensor (15 b) isinstalled along a gasket diagonal (16). FIG. 2 shows the gasket diagonal(16) extending from the top of the left upper port (11 a) on the thirdplate (5 c) towards the longitudinal right edge (9) at the underside ofthe upper right port (11 b). With this positioning, it is desirable thatthe sensor (15 b) be located on the portion of the gasket diagonal (16)which is situated to the right of the centreline (14) of the plate (5c). The fact that plates are normally equipped with suspension devices(17) situated in the region between the upper ports (11 a and 11 b)makes it undesirable for sensors to be located on the portion of thegasket diagonal (16) which is nearest to the suspension devices (17) andwhich extends to the left of the centreline (14). This undesirability isbecause access to the sensors would then be difficult.

A second sensor (15 d), see FIG. 1, is located at any desired pointalong the flow path of the fluid to the heat exchanger (2) from the lastcomponent (18), as seen in the direction of flow, of the heat exchangersystem (1). The last component (18) of the heat exchanger system (1) isdefined as the last component (18) which has the possibility ofinfluencing the characteristic of the fluid entering the heat exchanger(2) e.g. the pressure. As previously mentioned, this last component (18)may for example take the form of a pump which supplies the heatexchanger (2) with fluid.

In the preferred embodiment of the invention, the aforesaid secondsensor (15 d), see FIG. 1, is located in such a way that the hot fluidentering the heat exchanger is monitored. This is because the pressureof the hot fluid relative to the gasket pressure in the channel for thehot fluid is crucial to being able to assess whether there is risk ofleakage. Where so required by applications in which it is desirable tobe able to register the incoming cold fluid, a sensor is located in sucha way that the incoming cold fluid is monitored. The gasket pressure inthe channel for the cold fluid is then monitored in a correspondingmanner.

FIG. 2 indicates a space (19) formed between the frame plate (3) and thefirst plate (5 a). This space (19) is drained and constitutes aninsulating layer whereby the fluid flowing in a first channel (20 a)(between the first and second plates (5 a and 5 b)) only has heattransfer with the fluid flowing in a second channel (20 b) formedbetween the second and third plates (5 b and 5 c).

According to the preferred embodiment of the invention, the channelsalternately contain cold and hot fluid, thus the first channel (20 a)contains cold fluid, the second channel (20 b) contains hot fluid, andso on.

In a plate package provided with gaskets, the greatest gasket wear andthe greatest probability of gaskets failing are in the channels situatedclosest to a frame plate or pressure plate, since the gaskets there aresubject to the highest temperatures and the greatest temperaturefluctuations. The different respective thermal expansion coefficients ofthe frame plate and the pressure plate result in friction between thevarious plates, the gaskets, the frame plate and the pressure platebecause they move differently in response to, for example, temperaturefluctuations. Thus plates situated close to the frame plate and pressureplate do not adapt as easily to such movements as do plates located inthe middle of a plate package, where all the plates situated closetogether move in a similar way. The aforesaid movements thereforecontribute to the greatest risk of gasket failure being in the channelwhich first receives the incoming hot fluid and is located nearest to aframe plate or pressure plate.

The foregoing reasoning makes it clear why in the preferred embodimentof the invention the sensor (15 a), see FIG. 2, is located in the upperleft region of the plate (5 c), below the upper left port (11 a). Thisis the region in which the highest temperature prevails and such factorsas thermal expansion coefficients impart to the mutually adjacent plates(5 a-5 c) and the frame plate (3) the greatest mutual mobility, therebycontributing to major stresses. The gasket (6) in this region is alsoexposed to oxygen action from the outside of the heat exchanger (2).

During operation, the plate heat exchanger provided with gasketsaccording to the invention functions in the following manner.

The sensor (15 a) monitors the pressure which the gasket (6) and theplate (5 c) exert upon one another. As previously mentioned, hot fluidenters from the upper left port on the third plate (5 c) and isdistributed in the second channel (20 b). The pressure of the incomingfluid is monitored before the fluid is distributed out among the platesin the manner previously mentioned, viz. at any desired point along thefluid's flow path to the heat exchanger (2) from the last component (18)of the heat exchanger system (1), see FIG. 1.

The measured values from the sensors are registered and processed in aconventional processor. The processor monitors inter alia that thepressure of the fluid does not exceed the pressure which the gasket (6)and the plate (5 c) exert upon one another. If the pressure of the fluidis greater than the gasket pressure, it means that risk of leakagethrough or round the gaskets (6) may arise. The values obtained for thepressure of the fluid and the gasket pressure are used for calculating aratio between them which is a so-called differential pressure value. Ifchanges in said differential pressure value exceed permissible limitvalues, also called set-values, an indicator is activated. The purposeof the indicator is to attract attention so that the process can behalted and the system can be subjected to necessary servicingoperations.

In another alternative embodiment of the invention, a sensor (15 c) islocated on a second plate (5 b) instead of on the third plate (5 c). Thesensor is situated between the gasket (6) and the plate (5 b) in thesame way as previously explained. The sensor (15 c) is thus located atthe upper left region of the second plate (5 b, see FIG. 2), under thegasket (6) along the longitudinal left edge (8), lower than the upperleft port (5 a), and above the gasket diagonal (16). As the sensor (15c) is connected to the second plate (5 b), the sensor (15 c) also reactsto pressure changes taking place on the side of the second plate (5 b)which is adjacent to the third plate (5 c).

In a further alternative embodiment of the invention (not depicted inthe drawings) a fragment of a gasket is placed in an environmentcorresponding to that prevailing in the aforesaid heat exchangers. Suchsimulation of the heat exchangers gasket situation makes it possible tobe able to supervise and assess the risk of fluid leakage through agasket located in the heat exchanger without any need to be in theimmediate vicinity of the heat exchanger.

The invention is not limited to the embodiment referred to but may bevaried and modified within the scopes of the claims set out below, ashas been partly described above.

1. A method for assessing, in a heat exchanger having a number of heatexchanger plates and intermediate gaskets therebetween, thefunctionality of a gasket material comprising using a first sensor tomonitor a compression pressure of a gasket material, registering andprocessing in a processor a value monitored by the first sensor toassess an associated risk of leakage of a fluid flowing through the heatexchanger, comparing the value monitored with a predetermined set-valueand in the event of deviation between the monitored value and thepredetermined set-value, activating an indicator before leakage throughor past the gasket occurs.
 2. A method according to claim 1 furthercomprising using the value monitored to derive a ratio to compare with apredetermined set-value.
 3. A method according to claim 1, furthercomprising monitoring a pressure of the fluid.
 4. A method according toclaim 3, wherein the pressure of the fluid is monitored by a secondsensor.
 5. A method according to claim 3, wherein the pressure of thefluid relative to the gasket material is monitored by a second sensor.6. A method according to claim 4, wherein at least one of the sensorshas fluid contact with the fluid of the heat exchanger.